This invention is generally directed to processes for the preparation of polymers, especially toner resin polymer compositions. In one embodiment, the present invention is directed to processes for the preparation of polymers by suspension polymerization wherein there is initially formed an aqueous phase containing a surfactant, thereafter adding monomers thereto and initiating polymerization, subsequently adding a stabilizer such as tricalcium phosphate, and completing the polymerization. Another embodiment of the present invention relates to the preparation of polymers, such as styrene butadiene toner polymers comprising forming by, for example, mixing an aqueous phase containing a surfactant or emulsifier, such as ALKANOL.TM., like an alkali alkyl naphthalene sulfonate; thereafter adding monomers thereto, initiating polymerization thereof; subsequently adding a stabilizer such as tricalcium phosphate, and completing the polymerization. One advantage associated with the process of the present invention resides in a reduction in the amount of undesirable ash containing, for example, tricalcium phosphate, for example in some embodiments up to 50 percent less ash is obtained as compared to, for example, some present suspension polymerization processes. With standard known suspension polymerizations for the preparation of toner polymers such as styrene butadiene copolymers, reference U.S. Pat. No. 4,558,108, the disclosure of which is totally incorporated herein by reference, tricalcium phosphate stabilizers can be added to the aqueous phase prior to the polymerization of the reaction mixture resulting in polymers that may have undesirable amounts of ash. It is believed that the residual ash remaining from the suspension stabilizer tricalcium phosphate with the aforementioned suspension polymerization may, for example, chemically interact with the charge enhancing additives selected for the toner resulting in an undesirable rapid admix behavior degradation with aging, a disadvantage avoided or minimized with the process of the present invention.
The polymers obtained with the process of the present invention can be formulated into toners by, for example, the addition thereof to pigments or dyes, optional additives such as charge control materials, low molecular weight waxes such as polypropylene, polyethylene, and the like. Also, the toner composition obtained can be optionally blended with surface additives, which may function as flow aids, such as colloidal silicas and the like.
The preparation of toner polymers by suspension polymerization, emulsion polymerization, and other similar methods are known, reference the suspension method disclosed in the aforementioned '108 patent. In these processes, especially the suspension polymerization, there is selected a stabilizer component, such as tricalcium phosphate, which stabilizes the suspension and prevents substantial bead sticking. Toners can then be generated by mixing the formed polymer with pigments in a melt mixing apparatus or an extrusion device. With the processes of the present invention, in embodiments thereof suspension polymerization is accomplished by preparing an aqueous phase comprised of water and a surfactant such as ALKANOL.TM.; heating this phase to an effective temperature of, for example, 95.degree. C.; adding the desired monomers such as styrene and butadiene together with polymerization initiators such as benzoyl peroxide and TBEC (O,O-t-butyl-O(2-ethylhexyl)monoperoxy-carbonate), whereby there is formed a suspension of monomer droplets in the aqueous solution; initiating polymerization; adding a suspension stabilizer, such as tricalcium phosphate; and thereafter completing polymerization by heating. Since particle formation and polymerization are initiated prior to the addition of the stabilizer, it is believed that a substantial decrease in trapped stabilizer inside the polymer particles occurs resulting in, for example, an ash content of from about 0.005 percent to 0.03 percent in embodiments of the present invention. In contrast, with the aforementioned prior art suspension polymerization process there is first formed an aqueous phase of water, tricalcium phosphate, and ALKANOL.TM.; thereafter heating the formed mixture; adding monomers, such as styrene and butadiene together with an initiators such as benzoyl peroxide and TBEC (O,O-t-butyl-O(2-ethylhexyl)monoperoxy-carbonate); forming a suspension that entraps some of the stabilizer; heating, for example, to 95.degree. C. forming a styrene butadiene copolymer with an undesirable high ash content (TCP), that is for example the ash content is from about 0.04 percent to about 0.15 percent.
Dispersion polymerization, suspension polymerization, emulsion polymerization, and the like are known. Disclosed in U.S. Pat. No. 4,486,559 is the preparation of a toner composition by the incorporation of a prepolymer into a monomer/pigment mixture, followed by emulsion polymerization. Also, methods of preparing toner, including suspension/dispersion polymerization, are illustrated in this patent. In these processes, the pigment and additives such as charge control components are added to a monomer or comonomers prior to polymerization. Particle formation is achieved by the dispersion of the pigmented monomer or comonomers in a continuous phase such as water, and the droplets of pigmented monomers are then polymerized to form toner particles. One advantage of these processes as compared to some other known methods is the elimination of fusion mixing (Banbury/extruder) and pulverization classification processing. With these processes, undesirable ash content can result causing toners with the polymers prepared to exhibit undesirable admix characteristics as indicated herein.
In a patentability search report the following United States patents were listed: U.S. Pat. No. 4,528,321 which discloses a polymer dispersing system comprising a polymerization stabilizer and a nonionic compound, which compound may include alkanols, polyalkylene glycol monoethers, alkonates, and benzyl alcohol, reference for example column 3; U.S. Pat. No. 4,659,641 discloses an improved process for the preparation of resin particles by bead polymerization, see the Abstract of the Disclosure for example; and U.S. Pat. No. 4,816,366 which discloses processes for the preparation of toners by certain suspension polymerization methods, see for example the Abstract of the Disclosure, and column 3. The disclosures of each of the aforementioned patents are totally incorporated herein by reference.
In U.S. Pat. No. 4,507,378 there is illustrated a process for the preparation of toner compositions for electrophotography which involves polymerizing an aqueous suspension of a monomer such as styrene in the presence of a dispersant which includes a phosphate compound. According to the disclosure of this patent, once polymerization occurs the dispersant is removed by adding a dilute acid and a final product is obtained subsequent to rinsing with water.
Furthermore, in U.S. Pat. No. 4,659,641, the disclosure of which is totally incorporated herein by reference, there is illustrated a polymerization process for toner resin compositions, reference Example I, wherein a styrene n-butyl methacrylate copolymer with 2 percent wax is dispersed in water. A suspending agent, tricalcium phosphate, and a surfactant in a monomer solution can be added to the initial mixture with a polymerization initiator such as benzoylperoxide. After polymerization occurs, nitric acid is added to remove the tricalcium phosphate and the final product is filtered, washed, and dried.
In U.S. Pat. No. 4,894,309, the disclosure of which is totally incorporated herein by reference, there is illustrated a polymerization process for the preparation of crosslinked copolymers for toner resin compositions, reference Example I, wherein a styrene butadiene copolymer crosslinked with divinylbenzene is formed in an aqueous phase of tricalcium phosphate and ALKANOL.TM.. After polymerization occurs, nitric acid is added to remove the tricalcium phosphate and the final product is filtered, washed, and dried.
Although the above-mentioned processes for preparing polymer particles useful in toner compositions are suitable for their intended purposes in most instances, there remains a need for other processes wherein there can be obtained products of high purity, that is for example with ash contents of less than 0.1 percent for example.